(function() {

    var root = (typeof exports == 'undefined' ? window : exports);

    var config = {
        // Ensure Content-Type is an image before trying to load @2x image
        // https://github.com/imulus/retinajs/pull/45)
        check_mime_type: true
    };



    root.Retina = Retina;

    function Retina() {}

    Retina.configure = function(options) {
        if (options == null) options = {};
        for (var prop in options) config[prop] = options[prop];
    };

    Retina.init = function(context) {
        if (context == null) context = root;

        var existing_onload = context.onload || new Function;

        context.onload = function() {
            var images = document.getElementsByTagName("img"), retinaImages = [], i, image;
            for (i = 0; i < images.length; i++) {
                image = images[i];
                retinaImages.push(new RetinaImage(image));
            }
            existing_onload();
        }
    };

    Retina.isRetina = function(){
        var mediaQuery = "(-webkit-min-device-pixel-ratio: 1.5),\
                      (min--moz-device-pixel-ratio: 1.5),\
                      (-o-min-device-pixel-ratio: 3/2),\
                      (min-resolution: 1.5dppx)";

        if (root.devicePixelRatio > 1)
            return true;

        if (root.matchMedia && root.matchMedia(mediaQuery).matches)
            return true;

        return false;
    };


    root.RetinaImagePath = RetinaImagePath;

    function RetinaImagePath(path, at_2x_path) {
        this.path = path;
        if (typeof at_2x_path !== "undefined" && at_2x_path !== null) {
            this.at_2x_path = at_2x_path;
            this.perform_check = false;
        } else {
            this.at_2x_path = path.replace(/\.\w+$/, function(match) { return "@2x" + match; });
            this.perform_check = true;
        }
    }

    RetinaImagePath.confirmed_paths = [];

    RetinaImagePath.prototype.is_external = function() {
        return !!(this.path.match(/^https?\:/i) && !this.path.match('//' + document.domain) )
    }

    RetinaImagePath.prototype.check_2x_variant = function(callback) {
        var http, that = this;
        if (this.is_external()) {
            return callback(false);
        } else if (!this.perform_check && typeof this.at_2x_path !== "undefined" && this.at_2x_path !== null) {
            return callback(true);
        } else if (this.at_2x_path in RetinaImagePath.confirmed_paths) {
            return callback(true);
        } else {
            http = new XMLHttpRequest;
            http.open('HEAD', this.at_2x_path);
            http.onreadystatechange = function() {
                if (http.readyState != 4) {
                    return callback(false);
                }

                if (http.status >= 200 && http.status <= 399) {
                    if (config.check_mime_type) {
                        var type = http.getResponseHeader('Content-Type');
                        if (type == null || !type.match(/^image/i)) {
                            return callback(false);
                        }
                    }

                    RetinaImagePath.confirmed_paths.push(that.at_2x_path);
                    return callback(true);
                } else {
                    return callback(false);
                }
            }
            http.send();
        }
    }



    function RetinaImage(el) {
        this.el = el;
        this.path = new RetinaImagePath(this.el.getAttribute('src'), this.el.getAttribute('data-at2x'));
        var that = this;
        this.path.check_2x_variant(function(hasVariant) {
            if (hasVariant) that.swap();
        });
    }

    root.RetinaImage = RetinaImage;

    RetinaImage.prototype.swap = function(path) {
        if (typeof path == 'undefined') path = this.path.at_2x_path;

        var that = this;
        function load() {
            if (! that.el.complete) {
                setTimeout(load, 5);
            } else {
                that.el.setAttribute('width', that.el.offsetWidth);
                that.el.setAttribute('height', that.el.offsetHeight);
                that.el.setAttribute('src', path);
            }
        }
        load();
    }




    if (Retina.isRetina()) {
        Retina.init(root);
    }

})();
